1. Field of the Invention
The present invention relates to a plasma processing apparatus that processes, for example, a semiconductor wafer or a liquid crystal display (LCD) substrate by using plasma, and a temperature measuring method.
2. Description of the Related Art
Accurately measuring a temperature of a substrate, for example, a semiconductor wafer or a liquid crystal display (LCD) substrate, to be processed by using a plasma processing apparatus is very important in order to accurately control shapes, properties, and so on of films or holes formed on or in the semiconductor wafer or the LCD substrate based on the result of various processes such as film formation and etching. Accordingly, a temperature of a semiconductor wafer or a LCD substrate has been measured by using various conventional methods such as a temperature measuring method using a fluorescent thermometer for measuring a temperature of a rear surface of a substrate, a resistance thermometer, or the like.
Recently, a temperature measuring technology using a low-coherence interferometer which can directly measure a temperature of a substrate, which is difficult to do with the conventional temperature measuring methods, has been developed. Also, as the temperature measuring technology using the low-coherence interferometer, a technology has been suggested in which a light from a light source is divided into a measurement light for temperature measurement and a reference light by a first splitter, the measurement light is divided into n measurement lights by a second splitter, the n measurement lights are emitted to n measurement points, and interference between reflected lights of the n measurement lights and a reflected light of the reference light reflected by a reference light reflecting unit is measured to simultaneously measure temperatures of the plurality of measurement points (refer to, for example, Patent Reference 1). According to such a technology, temperatures of a plurality of measurement points may be simultaneously measured with a simple structure. Also, as a temperature measuring technology using the above-described low-coherence interferometer, a technology has been suggested in which a hole through which light passes is formed in a holding stage on which a substrate is mounted, an upper electrode, or the like, and a measurement light is vertically emitted to a surface of an object to be measured through the hole to measure a temperature of the object (refer to, for example, Patent Reference 2).
Also, a technology has been suggested in which a laser light is emitted via a peeping window of a vacuum film-forming apparatus, and a speckle pattern generated due to scattering reflection is received by using an image sensor to measure a temperature of a substrate by using a moving distance of the speckle pattern (refer to, for example, Patent Reference 3). However, this technology is not a temperature measuring technology using a low-coherence interferometer.
As described above, when a temperature of an object to be measured in a processing chamber is measured during a plasma process by using a temperature measuring technology using a low-coherence interferometer, a hole through which light passes is formed in a holding stage on which a substrate is mounted or an upper electrode, and a measurement light is vertically emitted to a surface of the object to be measured to measure the temperature of the object to be measured. However, as such, if the hole is formed in the holding stage or the upper electrode of a plasma processing apparatus, it may negatively affect uniformity of the plasma process.    [Patent Reference 1] Japanese Laid-Open Patent Publication No. 2006-112826    [Patent Reference 2] Japanese Laid-Open Patent Publication No. 2010-199526    [Patent Reference 3] Japanese Laid-Open Patent Publication No. hei 10-19690